In recent years gas discharge display panels such as plasma display panels (PDPs) have been attracting interest as display apparatuses for use in computers, television and the like due to their suitability as thin, light large-screen display devices.
FIG. 1 is a schematic diagram of a common alternating current (AC) PDP.
As the diagram shows, a PDP 100 is composed of a front plate 90 and a back plate 91 that are arranged with their main surfaces facing each other.
The front plate 90 is made up of a front glass substrate 101, display electrodes 102, a dielectric layer 106, and a protective layer 107.
The front glass substrate 101 is the material that is the base of the front plate 90, and the display electrodes 102 are formed on this front glass substrate 101.
Each display electrode 102 includes a transparent electrode 103, a black electrode film 104, and a bus electrode 105.
The display electrodes 102 and the front glass substrate 101 are further covered with the dielectric layer 106 and the protective layer 107.
The back panel 91 includes a back panel substrate 111, address electrodes 112, a dielectric layer 113, barrier ribs 114, and phosphor layers 115 formed in the gaps between neighboring barrier ribs 114. Hereinafter these gaps are referred to as barrier rib channels.
The front plate 90 and the back plate 91 are placed together and sealed as shown in FIG. 1, thus forming discharge spaces 116 inside.
Note that in the present drawing the end of the back plate 91 is illustrated as being open for convenience in explaining the structure. In reality the periphery is sealed closed.
Discharge gas (enclosed gas) made up of a rare gas component such as He, Xe or Ne is enclosed in the discharge space 116 at a pressure of approximately 500 Torr to 600 Torr (66.5 kPa to 79.8 kPa).
Areas where a pair of neighboring display electrodes 102 and one address electrode 112 intersect surrounding a discharge space 116 are cells that contribute to image display.
FIG. 2 shows the structure of a plasma display apparatus that is one type of gas discharge display apparatus.
This plasma display apparatus is composed of a PDP 100 and a panel driving device 119.
In this plasma display apparatus, address discharge is performed by applying voltage across the X electrode and the address electrode 112 of the cell that is to be illuminated, and then sustain discharge is performed by applying a pulse voltage to the pair of neighboring display electrodes 102.
In the PDP 100, this sustain discharge generates ultraviolet light in the discharge cell 116. The ultraviolet light hits the phosphor layer 115 and is converted to visible light, resulting in the cell being illuminated. This is how an image is displayed.
The front glass substrate 101 is subject to baking in the process for forming the black electrode film 104 and the bus electrode 105 and the process for forming the dielectric layer 106.
Furthermore, in the processes for forming the address electrodes 112, the dielectric layer 113, the barrier ribs 114, and the phosphor layer 115, the back glass substrate 111, on which these materials have been applied, is subject to baking.
In the baking processes, each of the front glass substrate 101 and the back glass substrate 111 (hereinafter “glass substrate” refers to either one), on which the black electrode film 104, the dielectric layer 113, or another of the materials to be baked has been disposed, is placed on a setter 120 and baked. The setter 120 is a heat resistant material that is in the shape of a plate that is larger than the size of the glass substrates.
The setter 200, on which the glass substrate has been placed, is carried through a continuous baking oven by hearth rollers 130, and baked at a temperature profile in which the peak temperature is set at, for example, 590° C.
However, the following problems occur during the heating process.
As shown in FIG. 4, the front glass plate 101 or the back glass plate 111 is placed in the correct position while at room temperature, but moves from the correct position (hereinafter call “misalignment”) during baking. This gives rise to the problem that the material that is baked, such as the dielectric layer, on the front glass plate 101 or the back glass plate 111 is not baked at an even temperature, and unevenness of temperature distribution occurs.
Misalignment tends to happen more frequently the larger the size of the front glass substrate 101 and the back glass substrate 111.
There are cases in which the normal characteristics of the materials cannot be obtained when baking is imperfect due to the materials not being baked at an even temperature.
For example, when baking of the dielectric layer 106 is imperfect, organic compounds such as resin are insufficiently removed and remain in the dielectric layer, thus making it difficult to ensure normal transparency and insulation characteristics.
Furthermore, when baking of the barrier ribs 114 is imperfect, the barrier ribs 114 lack strength, and may exhibit cracking or the like. In addition, the surfaces of imperfectly baked barrier ribs 114 have are uneven, and consequently prevent the phosphor layer 115 from being applied with even film thickness to the surfaces of the barrier ribs 114 in a later process.
In other words, problems in the quality of the gas discharge display panels can occur due to the baking processes.